We have developed hemagglutination methods for the study of lipoproteins-glycosaminoglycans interaction and have demonstrated that the interaction occurs with the aproprotein part of the lipoproteins and its is a function of the molecular structure and degree of sulfation of the glycosaminoglycans. Thus, different types of glycosaminoglycans may interact with lipoproteins, if those structural requirements are met. In line with this hypothesis, we have prepared substrates aand developed methods for the measurements of several GAG sulfatases, since it is possible that their functional decline might cause an increase of GAG capable of interacting with lipoproteins. These methods have allowed us to define the enzymic defect responsible for Morquio disease and to describe a new mucopolysaccharidosis. With the aid of the hemagglutination methods and with the use of a LDL-affinity column, we have attempted the isolation of the LDL receptor of human skin fibroblasts. Cultured skin fibroblasts, grown in presence of 3H-leucine and 35SO4 have been treated with collagenase and then with trypsin. These digests have been applied to the affinity column which has been eluted with 0.5 M KC1, 2.5 M KC1 and 2.5 M KI. The latter eluate, after dialysis and lyophilization, shows ability to agglutinate LDL-coated red cells and it is labeled with 3H-leucine and 35SO4.